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          <h1>Writing Verticles</h1>
          
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<div id="content">
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          <ul class="sectlevel2">
<li><a href="#_writing_verticles">Writing Verticles</a></li>
<li><a href="#_accessing_the_vertx_instance_from_a_verticle">Accessing the vertx instance from a verticle</a></li>
<li><a href="#_asynchronous_verticle_start_and_stop">Asynchronous Verticle start and stop</a></li>
</ul>
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      <div class="col-sm-12 col-md-pull-3 col-md-9">
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          <h2>Table of Contents</h2>
          <ul class="sectlevel2">
<li><a href="#_writing_verticles">Writing Verticles</a></li>
<li><a href="#_accessing_the_vertx_instance_from_a_verticle">Accessing the vertx instance from a verticle</a></li>
<li><a href="#_asynchronous_verticle_start_and_stop">Asynchronous Verticle start and stop</a></li>
</ul>
        </div>
        <div class="sect2">
<h3 id="_writing_verticles">Writing Verticles</h3>
<div class="paragraph">
<p>There are three alternatives to create verticles in Groovy:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>a plain Groovy script</p>
</li>
<li>
<p>a Groovy class extending the <code>GroovyVerticle</code> class</p>
</li>
<li>
<p>a Groovy class implementing the <code>Verticle</code> interface or extending the <code>AbstractVerticle</code> class</p>
<div class="literalblock">
<div class="content">
<pre>We will not cover the third case in this manual, as it is a plain Java class and instead you should read the
Vert.x manual for Java.</pre>
</div>
</div>
</li>
</ul>
</div>
<div class="paragraph">
<p>For example, the next snippet is a valid Groovy verticle:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">println "Hello from vertx"</code></pre>
</div>
</div>
<div class="paragraph">
<p>On deployment, by default, Vert.x executes the script. Optionally, your script can provide the <code>startVertx</code> and
<code>stopVertx</code> methods. Theses methods are called respectively when the verticle starts and stops:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">void vertxStart() {
 println "starting"
}

void vertxStop() {
 println "stopping"
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Alternatively, you can extend the <code>GroovyVerticle</code> class and implement the <code>start</code> and
<code>stop</code> methods:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">import io.vertx.lang.groovy.GroovyVerticle;

public class HelloWorldHttpVerticle extends GroovyVerticle {

 public void start() {
  println("Starting")
 }

 public void stop() {
   println("Stopping")
 }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>As in Java, vert.x creates a new instance of the class automatically.  When Vert.x deploys the verticle it will call
the <code>start</code> method, and when the method has completed the verticle will be considered started.</p>
</div>
<div class="paragraph">
<p>You can also optionally override the <code>stop</code> method. This will be called by Vert.x when the verticle is undeployed
and when the method has completed the verticle will be considered stopped.</p>
</div>
</div>
<div class="sect2">
<h3 id="_accessing_the_vertx_instance_from_a_verticle">Accessing the vertx instance from a verticle</h3>
<div class="paragraph">
<p>Regardless the way you use to implement your verticle, you access the vert.x instance using the <code>vertx</code> variable /
field.</p>
</div>
<div class="listingblock">
<div class="title">Access to the vert.x instance in a Groovy script</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">vertx.deployVerticle("another_verticle.rb")</code></pre>
</div>
</div>
<div class="listingblock">
<div class="title">Access to the vert.x instance in a Groovy class</div>
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">import io.vertx.lang.groovy.GroovyVerticle;

public class HelloWorldHttpVerticle extends GroovyVerticle {

   public void start() {
     vertx.deployVerticle("another_verticle.js")
   }
}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_asynchronous_verticle_start_and_stop">Asynchronous Verticle start and stop</h3>
<div class="paragraph">
<p>Sometimes you want to do something in your verticle start-up which takes some time and you don&#8217;t want the verticle to
be considered deployed until that happens. For example you might want to deploy other verticles in the start method.</p>
</div>
<div class="paragraph">
<p>You can&#8217;t block waiting for the other verticles to deploy in your start method as that would break the <a href="#golden_rule">Golden Rule</a>.</p>
</div>
<div class="paragraph">
<p>So how can you do this?</p>
</div>
<div class="paragraph">
<p>The way to do it is to implement the <strong>asynchronous</strong> start method. This version of the method takes a Future as a parameter.When the method returns the verticle will <strong>not</strong> be considered deployed.</p>
</div>
<div class="paragraph">
<p>Some time later, after you&#8217;ve done everything you need to do (e.g. start other verticles), you can call complete
on the Future (or fail) to signal that you&#8217;re done. Similarly, there is an asynchronous version of the stop method too.
You use this if you want to do some verticle cleanup that takes some time.</p>
</div>
<div class="paragraph">
<p>When your verticle is implemented as a script, asynchronous start and stop are implemented as follows:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">import io.vertx.groovy.core.Future

void vertxStart(Future&lt;Void&gt; future) {
 println "starting"
 vertx.deployVerticle("v.rb", { res -&gt;
   if (res.succeeded()) {
     future.complete()
   } else {
     future.fail()
   }
 })
}

void vertxStop(Future&lt;Void&gt; future) {
 println "stopping"
 future.complete()
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>If your verticle extends <code>GroovyVerticle</code>, you override the
<code>start</code> and
<code>stop</code> methods:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">import io.vertx.core.Future
import io.vertx.lang.groovy.GroovyVerticle

public class HelloWorldHttpVerticle extends GroovyVerticle {
 public void start(Future&lt;Void&gt; future) {
   println "starting"
   vertx.deployVerticle("v.rb",
   { res -&gt;
     if (res.succeeded()) {
       future.complete()
     } else {
       future.fail()
     }
   })
  }

 public void stop(Future&lt;Void&gt; future) {
  println("stopping")
  future.complete()
 }
}</code></pre>
</div>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<div class="title">Important</div>
</td>
<td class="content">
Notice that depending your implementation choice, the <code>Future</code> class is different. Groovy verticle
implemented as script are using <code>io.vertx.groovy.core.Future</code>, while classes are using
<code>io.vertx.core.Future</code>
</td>
</tr>
</table>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
You don&#8217;t need to manually undeploy child verticles started by a verticle, in the verticle&#8217;s stop method.
Vert.x will automatically undeploy any child verticles when the parent is undeployed.
</td>
</tr>
</table>
</div>
</div>

        

        
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